1. Field Of The Invention
This invention relates to heat transfer apparatus especially useful for cooling electronic components.
2. Description Of The Related Art
Cooling of electric devices including electronic components such as integrated circuits is often accomplished by the use of fans, passive heat sinks, or both. Fans provide forced-air convection cooling, but may produce an unacceptable level of noise. Passive heat sinks dissipate thermal energy from components by conduction, but require a certain volume which may be difficult to provide within compact or densely arranged electronic systems.
A recent development that has been found to efficiently transfer heat in compact electronic systems is the thermal transfer bag, also known as the Liquid Heat Sink bag available from Minnesota Mining and Manufacturing Company, assignee of the present invention. The bag is made of a flexible sheet of material, and has an inner, closed compartment that is filled with a thermally conductive, chemically inert, essentially gas free body of liquid which comprises fluorochemical liquid. The bag is placed between a heat-generating component and a heat-dissipating surface of a heat sink, and thermal conduction through the liquid as well as some convective currents of liquid within the closed chamber of the bag transfer heat from the component to the heat sink.
The aforementioned thermal transfer bag is advantageous in that the flexible material geometrically conforms to the shape of the cavity between the component and the heat sink within the electronic equipment, and readily establishes intimate contact with the heat-generating component and the heat-dissipating surface to establish a thermal path therebetween. In some applications, the inherent shock-absorbing nature of the filled bag functions as a packing or cushion to protect the component from physical shock damage. The bag can easily be removed and replaced in the field during repair of the equipment, and may optionally be provided with an adhesive to retain the bag in a particular location.
However, it is sometimes difficult to provide sufficient space for passive heat sinks with such thermal transfer bags in certain electronic equipment having components that produce relatively large amounts of heat, particularly where a number of heat-producing components are spaced closely together. In such circumstances, an active, flow-through liquid cooling system may be considered, so that the flowing fluid may be used to transfer heat to a heat sink (such as a chilled water supply, refrigeration system or liquid-to-air heat exchanger) remote from the heat source.
One type of flow-through cooling apparatus for integrated circuits is described in IBM Technical Disclosure Bulletin, Vol. 28, No. 3 (August 1985). The aforementioned reference describes a coolant compartment with a flexible wall, and a metal plate attached to the wall contacts a multi-chip module and includes a number of studs that extend through the wall and into the coolant to act as fins. While this type of apparatus has certain advantages over passive heat transfer devices, there is a continuing need to improve the efficiency of heat transfer of active heat transfer apparatus for electrical devices, and also provide apparatus that is sufficiently rugged to withstand repeated handling and yet is adaptable for use in a variety of electronic devices.